The recharging of primary batteries is frequently discouraged by battery manufacturers. Thus, for example, on page 2 of a publication entitled "Eveready Battery Engineering Data" (Union Carbide Corporation, New York, 1968), a warning is made that "IF `EVEREADY` PRIMARY BATTERIES ARE SUBJECTED TO ANY FORM OF RECHARGING, ALL WARRANTIES . . . ARE NULL AND VOID. NOTE THE DISCUSSION ON PAGE 23."
Page 23 of the Union Carbide publication discloses that, under certain limited conditions, one may recharge a primary battery. Quoting the National Bureau of Standards (letter circular LC965), the publication states that: "Although the dry cell is nominally considered a primary battery it may be recharged for a limited number of cycles under certain conditions. 1. The operating voltage on discharge should not be below 1.0 volt per cell when battery is removed from service for charging. 2. The battery should be placed on charge very soon after removal from service. 3. The ampere-hours of recharge should be 120%-180% of the discharge. 4. Charging rate should be low enough to distribute recharge over 12-16 hours. 5. Cells must be put into service soon after charging as the recharged cells have poor shelf life."
As is disclosed by this Union Carbide publication, the prior art method for recharging primary batteries is unattractive. In the first place, an operating voltage on discharge above 1.0 volt severely limits the available energy which can be withdrawn from the battery, representing only shallow discharge. In the second place, it is not always possible to place a battery on charge very soon after removal from service. In the third place, end users of batteries often are unwilling to recharge a battery for a prolonged period of up to 16 hours, preferring shorter recharging cycles. In the fourth place, the recharged batteries produced by the prior process have poor shelf life.
It is an object of this invention to provide a battery charger for recharging primary batteries which can permit an operating voltage on discharge substantially below 1.0 volt.
It is another object of this invention to provide a battery charger for recharging primary batteries which minimizes the adverse effect of delayed recharging.
It is yet another object of this invention to provide a battery charger which can effectively recharge a primary battery in as little as about 8 hours.
It is yet another object of this invention to provide a battery recharger which will provide recharged primary batteries with substantially improved shelf lives.
It is yet another object of this invention to provide a battery recharger suitable for recharging rechargeable alkaline-manganese ("RAM") batteries.
It is yet another object of this invention to provide a battery recharger suitable for recharging rechargeable nickel-cadmium batteries, and also ordinary carbon-zinc batteries.
It is yet another object of this invention to provide a battery charger suitable for recharging batteries containing lithium and thionyl chloride.
It is yet another object of this invention to provide a battery charger suitable for recharging lithium-sulfur batteries.
It is yet another object of this invention to provide a battery charger equipped with visual means for displaying after whether a battery has been rejuvenated sufficiently to power a standard load for a fixed period and maintain a voltage above a test threshold.